This invention relates to a catalytic hydrocracking process for upgrading hydrocarbon streams.
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure as determined by X-ray diffraction, within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties. Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline silicates. These silicates can be described as a rigid three-dimensional framework of SiO.sub.4 and Periodic Table Group IIIA element oxide, e.g. AlO.sub.4, in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total Group IIIA element, e.g. aluminum, and silicon atoms to oxygen atoms is 1:2. The electrovalence of the tetrahedra containing the Group IIIA element, e.g. aluminum, is balanced by the inclusion in the crystal of a cation, e.g. an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of the Group IIA element, e.g. aluminum, to the number of various cations, such as Ca/2, Sr/2, Na, K or Li, is equal to unity. One type of cation may be exchanged either entirely or partially with another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given silicate by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
Prior art techniques have resulted in the formation of a great variety of synthetic zeolites. Many of these zeolites have come to be designated by letter or other convenient symbols, as illustrated by zeolite Z (U.S. Pat. No. 2,882,243); zeolite X (U.S. Pat. No. 2,882,244); zeolite Y (U.S. Pat. No. 3,130,007); zeolite ZK-5 (U.S. Pat. No. 3,247,195); zeolite ZK-4 (U.S. Pat. No. 3,314,752); zeolite ZSM-5 (U.S. Pat. No. 3,702,886); zeolite ZSM-11 (U.S. Pat. No. 3,709,979); zeolite ZSM-12 (U.S. Pat. No. 3,832,449); zeolite ZSM-20 (U.S. Pat. No. 3,972,983); zeolite ZSM-35 (U.S. Pat. No. 4,016,245); and zeolite ZSM-23 (U.S. Pat. No. 4,076,842), merely to name a few.
The SiO.sub.2 /Al.sub.2 O.sub.3 ratio of a given zeolite is often variable. For example, zeolite X can be synthesized with SiO.sub.2 /Al.sub.2 O.sub.3 ratios of from 2 to 3; zeolite Y, from 3 to about 6. In some zeolites, the upper limit of the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is unbounded. ZSM-5 is one such example wherein the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is at least 5 and up to the limits of present analytical measurement techniques. U.S. Pat. No. 3,941,871 (U.S. Pat. No. Re. 29,948) discloses a porous crystalline silicate made from a reaction mixture containing no deliberately added alumina in the recipe and exhibiting the X-ray diffraction pattern characteristic of ZSM-5. U.S. Pat. Nos. 4,061,724; 4,073,865 and 4,104,294 describe crystalline silicates of varying alumina and metal content.
The hydrocracking of hydrocarbons to produce lower boiling hydrocarbons, and in particular, hydrocarbons boiling in the motor fuel range, is an operation upon which a vast amount of time and effort has been spent in view of its commercial significance. Hydrocracking catalysts usually comprise a hydrogenation-dehydrogenation component deposited on an acidic support such as silica-alumina, silica-magnesia, silica-zirconia, alumina, acid treated clays, zeolites, and the like.
Zeolites have been found to be particularly effective in the catalytic hydrocracking of a gas oil to produce motor fuels and such has been described in many U.S. patents including U.S. Pat. Nos. 3,140,249; 3,140,251; 3,140,252; 3,140,253; and, 3,271,418.
A catalytic hydrocracking process utilizing a catalyst comprising a zeolite dispersed in a matrix of other components such as nickel, tungsten and silica-alumina is described in U.S. Pat. No. 3,617,498.
A hydrocracking catalyst comprising a zeolite and a hydrogenation-dehydrogenation component such as nickel-tungsten sulfide is disclosed in U.S. Pat. No. 4,001,106.
The hydrocracking process described in U.S. Pat. No. 3,758,402 utilizes a catalyst possessing a large pore size zeolite component such as zeolite X or Y and an intermediate pore size zeolite component such as ZSM-5 with a hydrogenation-dehydrogenation component such as nickel-tungsten being associated with at least one of the zeolites.
Hydrocarbon conversion utilizing a catalyst comprising a zeolite, such as ZSM-5, having a zeolite particle diameter in the range of 0.005 micron to 0.1 micron and in some instances containing a hydrogenation-dehydrogenation component is disclosed in U.S. Pat. No. 3,926,782.
The hydrocracking of lube oil stocks employing a catalyst comprising a hydrogenation component and a zeolite such as ZSM-5 is disclosed in U.S. Pat. No. 3,755,145.
Hydrocracking operations featuring the use of dual reaction stages, or zones, and/or two different catalysts are also known.
U.S. Pat. No. 3,535,225 discloses a dual-catalyst hydrocracking process in which a hydrocarbon feedstock is initially contacted with a first catalyst comprising a hydrogenation component and a component selected from the group consisting of alumina and silica-alumina and subsequently with a second catalyst provided as a silica-based gel, a hydrogenation component and a zeolite in the ammonia or hydrogen form and free of any loading metal or metals.
U.S. Pat. No. 3,536,604 discloses a hydrofining-hydrocracking process in which a hydrocarbon feed containing 300 to 10,000 ppm organic nitrogen is contacted with a hydrofining catalyst comprising a Group VI or Group VIII metal on an alumina or silica-alumina support whereby the organic nitrogen content of the feed is reduced to a level of 10 ppm to 200 ppm, a substantial portion of the resulting hydrofined effluent thereafter being contacted with a second catalyst comprising a gel matrix comprising at least 15 wt. % silica, alumina, nickel and/or cobalt, molybdenum and/or tungsten, and a zeolite in the ammonia or hydrogen form and free of any loading metal.
U.S. Pat. No. 3,536,605 discloses a hydrofining-hydrocracking process in which a hydrocarbon feed containing substantial amounts of organic nitrogen is contacted in a hydrofining reaction zone under hydrofining conditions with a catalyst comprising a gel matrix comprising silica and alumina and nickel and/or cobalt and molybdenum and/or tungsten and a zeolite having a silica-to-alumina ratio above about 2.15, a unit cell size below about 24.65 Angstroms (A), and a sodium content below about 3 wt. % to produce a hydrofined product of reduced nitrogen content. The effluent from the hydrofining reaction zone is then hydrocracked in a hydrocracking reaction zone under hydrocracking conditions in the presence of hydrogen and a hydrocracking catalyst.
U.S. Pat. No. 3,558,471 discloses a two-catalyst process wherein a hydrocarbon feedstock is first hydrotreated in the presence of a catalyst comprising a silica-alumina gel matrix containing nickel or cobalt, or both, and molybdenum or tungsten, or both, and a zeolite substantially in the ammonia or hydrogen form free of any catalytic loading metal or metals, the zeolite having a silica-to-alumina ratio above about 2.15, unit cell size below about 24.65 A, and a sodium content belwo about 3 wt. %, calculated as Na.sub.2 O, to produce a first effluent which is thereafter hydrocracked in a second reaction zone in the presence of a hydrocracking catalyst which may be the same catalyst used in the first reaction zone or a conventional hydrocracking catalyst.
U.S. Pat. No. 3,788,974 discloses a two-catalyst hydrocracking process wherein a hydrocarbon oil feedstock containing from about 0.01 to 0.5 wt. % nitrogen compounds is contacted in a first hydrocracking zone with a zeolite catalyst of the faujasite type in combination with a nickel/tungsten hydrogenation component to provide an effluent which is contacted in a second separate hydrocracking zone with a hydrocracking catalyst, preferably zeolite X or Y.
In U.S. Pat. Nos. 3,894,930 and 4,054,539, a hydrocracking process is disclosed which employs a catalyst comprising a hydrogenation component, an ultrastable zeolite and a silica-alumina cracking catalyst.
U.S. Pat. No. 4,612,108 discloses a process in which an initial hydrotreating stage employing a conventional hydrotreating catalyst is followed by a hydrocracking stage employing zeolite Beta as the hydrocracking catalyst.
Catalytic hydrocracking of a hydrocarbon feedstock can in certain cases be accompanied by dewaxing, that is selective conversion of straight-chain and slightly branched paraffins, such that the pour point of the product is reduced. See U.S. Pat. No. 3,668,113.
It is known to produce a high quality lube base stock oil by subjecting a waxy crude oil fraction to solvent refining, followed by catalytic dewaxing over ZSM-5, with subsequent hydrotreating of the lube base stock as described in U.S. Pat. No. 4,181,598. Zeolites such as ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35 , and ZSM-38 have been proposed for dewaxing processes and their use is described in U.S. Pat. Nos. 3,894,938; 4,176,050; 4,181,598; 4,222,855; 4,229,282; and 4,247,388. A dewaxing process employing synthetic offretite is described in U.S. Pat. No. 4,259,174.
The use of zeolite Beta as catalyst for dewaxing hydrocarbon feedstocks such as distillate fuel oils by isomerization is described in U.S. Pat. Nos. 4,419,220 and 4,501,926. U.S. Pat. No. 4,486,296 teaches hydrodewaxing and hydrocracking of a hydrocarbon feedstock over a three-component catalyst including zeolite Beta. Dewaxing a paraffin-containing hydrocarbon feedstock employing a hydrotreating step prior to the dewaxing step over zeolite Beta catalyst is disclosed in U.S. Pat. Nos. 4,518,485 and 4,612,108. U.S. Pat. No. 4,481,104 discloses distillate-selective hydrocracking using a large pore, high silica, low acidity catalyst, e.g. zeolite Beta catalyst. Hydrocracking C.sub.5.sup.+ naphthas over a catalyst comprising zeolite Beta is disclosed in U.S. Pat. No. 3,923,641. A dewaxing process using a noble metal/zeolite Beta catalyst followed by a base metal/zeolite Beta catalyst is disclosed in U.S. Pat. No. 4,554,065. U.S. Pat. No. 4,541,919 discloses a dewaxing process using a large pore zeolite catalyst such as zeolite Beta which has been selectively coked. U.S. Pat. No. 4,435,275 describes a moderate pressure hydrocracking process which may use a catalyst comprising zeolite Beta for producing low pour point distillates.
European patent application No. 94,827 discloses the use of zeolite Beta for hydrocracking and compares it for that process with other hydrocracking catalysts such as high silica zeolite Y, zeolite X and ZSM-20 (as described in European patent application No. 98,040). U.S. Pat. No. 4,612,108 describes the hydrocracking and dewaxing of waxy petroleum fractions by passing the fractions over a hydrocracking catalyst comprising zeolite Beta and a matrix material in the presence of hydrogen and under hydrocracking conditions, the proportion of zeolite Beta in the hydrocracking catalyst increasing in the direction in which the fraction is passed.
U.S. Pat. No. 4,601,993 describes the dewaxing of a lubricating oil feedstock by passing the waxy fraction over a catalyst bed containing a mixture of medium-pore size zeolite and large-pore zeolite having a Constraint Index of less than 2 and having hydroisomerization activity in the presence of a hydrogenation component.
U.S. Pat. No. 4,358,362 discloses a dewaxing process in which the feed is subjected to pretreatment with a zeolite sorbent to sorb zeolite poisons present therein.
It is known to produce lubricating oil of improved properties by hydrotreating the lubricating oil base stock in the presence of ZSM-39 containing cobalt and molybdenum, as shown in U.S. Pat. No. 4,395,327.